Refresh rate change requests to 40Hz are "adjusted" back to 60Hz

Bug #1848746 reported by Olivier Robert on 2019-10-18
This bug affects 1 person
Affects Status Importance Assigned to Milestone
linux (Ubuntu)

Bug Description

Dear Launchpad readers,

Changes to a 40Hz-based mode are adjusted back to a 60Hz display mode by KMS, as can be seen in the logs with the drm.debug=4 option :

oct. 18 16:27:24 NovHak-P2 kernel: [drm:intel_dump_pipe_config [i915]] requested mode:
oct. 18 16:27:24 NovHak-P2 kernel: [drm:drm_mode_debug_printmodeline [drm]] Modeline 0:"" 0 92450 1920 1968 2000 2080 1080 1083 1088 1111 0x0 0x9
oct. 18 16:27:24 NovHak-P2 kernel: [drm:intel_dump_pipe_config [i915]] adjusted mode:
oct. 18 16:27:24 NovHak-P2 kernel: [drm:drm_mode_debug_printmodeline [drm]] Modeline 0:"1920x1080" 60 140490 1920 1972 2007 2094 1080 1083 1089 1118 0x48 0x9

I managed to have 40Hz through EDID modification, swapping the two DTDs it contains, one being 60Hz, the other 40Hz, hence placing the 40Hz DTD first, but then it remains sticked to 40Hz and unable to switch to a 60Hz mode.

I suppose the bug is i915-related rather than Xorg-related, since the modelines seem correctly sent for KMS.

I can provide additional information if needed.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: linux-image-generic
ProcVersionSignature: Ubuntu 5.0.0-32.34-generic 5.0.21
Uname: Linux 5.0.0-32-generic x86_64
ApportVersion: 2.20.10-0ubuntu27.1
Architecture: amd64
 /dev/snd/controlC2: olivier 12097 F.... pulseaudio
 /dev/snd/controlC0: olivier 12097 F.... pulseaudio
 /dev/snd/controlC1: olivier 12097 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Fri Oct 18 16:43:01 2019
InstallationDate: Installed on 2019-09-22 (26 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
MachineType: Notebook P17SM-A
 PATH=(custom, no user)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.0.0-32-generic root=UUID=788f8a5e-9667-4cfb-abf4-bc76ebcb86bb ro quiet splash mtrr_spare_reg_nr=0 vt.handoff=1
 linux-restricted-modules-5.0.0-32-generic N/A
 linux-backports-modules-5.0.0-32-generic N/A
 linux-firmware 1.178.3
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install) 03/27/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 4.6.5
dmi.board.asset.tag: Tag 12345 P17SM-A
dmi.board.vendor: Notebook
dmi.board.version: Not Applicable
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr4.6.5:bd03/27/2014:svnNotebook:pnP17SM-A:pvrNotApplicable:rvnNotebook:rnP17SM-A:rvrNotApplicable:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.: Not Applicable P17SM-A
dmi.product.sku: Not Applicable
dmi.product.version: Not Applicable
dmi.sys.vendor: Notebook

Olivier Robert (novhak) wrote :

This change was made by a bot.

Changed in linux (Ubuntu):
status: New → Confirmed
Kai-Heng Feng (kaihengfeng) wrote :
Olivier Robert (novhak) wrote :

I'll switch to Eoan Ermine in the beginning of November and report back. Hopefully it will be enough !

Olivier Robert (novhak) wrote :

I made the switch to 19.10 and the problem is the same in the logs. There is a slight difference however, the screen doesn't flicker any more upon the change request. I suppose it now detects the adjusted modeline is the same as the current one, hence nothing to do.

Here's some output extracted from dmesg (ISO date format) :

2019-11-04T16:39:13,088276+01:00 [drm:intel_dump_pipe_config [i915]] requested mode:
2019-11-04T16:39:13,088290+01:00 [drm:drm_mode_debug_printmodeline [drm]] Modeline "": 0 92450 1920 1968 2000 2080 1080 1083 1088 1111 0x0 0x9
2019-11-04T16:39:13,088323+01:00 [drm:intel_dump_pipe_config [i915]] adjusted mode:
2019-11-04T16:39:13,088336+01:00 [drm:drm_mode_debug_printmodeline [drm]] Modeline "1920x1080": 60 140490 1920 1972 2007 2094 1080 1083 1089 1118 0x48 0x9

So it's the current 19.10 kernel (5.3.0-19-generic). I'm considering trying v5.4-rc5. I will report back once (and if) it's done.

Olivier Robert (novhak) on 2020-09-20
tags: added: eoan focal
Olivier Robert (novhak) wrote :

I switched to Focal in May and the bug is still there. The EDID workaround still works.

I must be the only one switching to 40Hz sometimes, or it only affects my GPU, which I doubt (Intel HD Graphics 4600, CPU Core i7-4710MQ).

Olivier Robert (novhak) on 2020-11-29
tags: added: groovy
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